Pumping system for oil burners



Dec. 7, 1965 s. KOFINK PUMPING SYSTEM FOR OIL BURNERS 5 Sheets-Sheet 1 Filed Oct. 25, 1962 n u n n /nvenfor SIEGFRIED KOF/NK G\ fly .mfinm,

Dec. 7, 1965 V s, KOHN'K 3,221,798

PUMPING SYSTEM FOR OIL BURNERS Filed 001',- 23, 1962 5 Sheets-Sheet 2 Fig.2

Dec. 7, 1965 s, oF 3,221,798

PUMPING SYSTEM FOR OIL BURNERS Filed Oct. 25, 1962 5 Sheets-Sheet 5 Fig. 3

Ir; vemor S/EGFR/ED KOF/NK Dec. 7, 1965 s. KOFINK PUMPING SYSTEM FOR OIL BURNERS 5 Sheets-Sheet 4 Filed 061;. 25, 1962 Fig.4

Fig. 6

Dec. 7, 1965 s. KOFINK PUMPING SYSTEM FOR OIL BURNERS 5 Sheets-Sheet 5 Filed Oct. 23, 1962 Altar/25245 H United States Patent 3,221,798 PUMPING SYSTEM FOR OIL BURNERS Siegfried Kofink, 8 Lenzhalde, Zell am Neckar, Germany Filed Oct. 23, 1962, Ser. No. 232,561 Claims priority, application Germany, Get. 26, 1961, K 45,042; May 25, 1962, K 46,840 4 Claims. (Cl. 15828) The present invention relates to an intermittently operated pumping system for oil burners.

Known systems employ fluid pumps wherein the moving element controls contacts governing the supply of electric current thereto. Such systems have the disadvantage, that the frequency of the periodic or reciprocating motion of the movable pumping element depends upon the load momentarily handled by the pump. Also, there is no possibility of adjusting this frequency.

It is an object of the present invention, to provide for a new and improved pulse operating electrically driven fluid pump system for oil burners in which the pulse frequency is adjustable independently from the pump load.

According to one aspect of the invention in a preferred embodiment thereof the following system is suggested.

The pump itself is defined by a suction and pressure chamber, the volume of which is being controlled by a spring biased armature cooperating for actuation with an electromagnet having a magnetizable coil. An electronic oscillator is provided producing as output a train of undirectional electric current pulses fed to the pump coil for energization thereof. The electronic oscillator includes a manually adjustable circuit element determining the frequency thereof. The electronic oscillator is to be of the relaxation type since the oscillation frequencies thereof are adjustable in the low frequency range including periods in the second or minute range or even longer. Preferably, an astable transistor multivibrator is employed producing very accurately rectangular current pulses. In a preferred arrangement, the pump is to convey oil to a burner, and a thermostat is provided to superimpose upon the oscillator intermittently control pulses so as to cause the pump to alternate between an average pulse frequency and a maximum frequency, the latter being associated with maximum pumping fluid (oil) output.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects, and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawing in which:

FIG. 1 illustrates a pulse controlled pumping system according to a preferred embodiment of the invention, illustrating in sectional view a pulse operated, electromagnetically actuated pump;

FIG. 2 illustrates the pulse source employed in the system of FIG, 1 for feeding current pulses to the electromagnet therein;

FIG. 3 illustrates a longitudinal section view of a modified form of an electromagentically actuated pump;

FIG. 4 illustrates a novel heating system controlled by a pump such as shown in FIG. 3;

FIG. 5 illustrates a circuit diagram of the controllable pulse source for producing current pulses for the electromagnet in the pump of FIGS. 3 and 4; and

FIG. 6 illustrates a circuit diagram of a modified detail of FIG. 5.

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Turning first to FIG. 1, there is shown a fluid pump having a housing 1 of hollow, cylindrical, i.e. tubular shape. Front and rear ends of housing 1 have annular flanges, and they are respectively closed by means of caps 2 and 3, whereby a membrane 4 is interposed between the left hand flange and cap 2, and a membrane 5 is interposed between the right hand flange and cap 3. The membranes are tensioned along their annular, circumferential margin, i.e., where directly sandwiched between the respective cap and flange.

An armature 6 is secured to the center of the left hand membrane 4, which armature 6 has an axially projecting rod 7 secured in similar fashion to the center of membrane 5. A magnetizing coil 3 surrounds armature 6 permitting play of the latter. Coil and armature are coaxially disposed in housing 1. When electric current is fed to the coil 8, it magnetizes a yoke 9 which is also secured to housing 1 and having a central bore receiving with play rod 7. Coil 8 with yoke 9 constitutes an electromagnet cooperating with armature 6.

A compression spring 10 is centrally interposed between cap 3 and membrane 5. The force exerted by spring 10 is preferably symmetrical to rod 7 with a coaxial resulting force. Whenever coil 8 and yoke 9 are energized, armature 6 is attracted and moves to the right against the force of spring 10. The current supply for coil 8 will be described more fully below, but it is presently sufiicient to point out, that this current supply is an intermittent and periodic one, which means, that upon occurrence of a current pulse in coil 8 armature 6 is attracted and moves to the right as stated. Whereas upon current interruption, spring 10 returns armature 6 to the left into the position illustrated in the drawing. The armature 6 is, thus, periodically moved back and forth at a frequency depending upon the rate of succession of the current pulses in coil 8.

Cap 3 and membrane 5 define a space or chamber 11 to which there is access only through a relatively small opening 12. When armature 6 oscillates, it forces the center of membrane 5 alternatingly to the right and to the left so that air is successively discharged from or sucked into space 11 through opening 12. This produces a damping effect for oscillating armature 6 dependent upon the size of opening 12. Opening 12 is preferably made adjustable by conventional means to adjust the rate of damping.

Between membrane 4 and cap 2 there is a corresponding chamber 13 which is connected to a distributor 14 via a central opening (not shown) in cap 2. Distributor 14 is of conventional design and has an inlet pipe 17 through which fluid enters in direction of arrow 15, whereas the fluid is discharged through pipe 20 in direction of arrow 16. Suction into chamber 13 from pipe 17 through distributor 14 occurs when armature 6 moves from left to right, and discharge of chamber 13 through distributor 14 and pipe 20 occurs when armature 6 moves in the reverse direction.

Between pipe 17 and distributor 14 there is interposed a check valve 18 governing chamber 13 accordingly, and permitting passage of fluid in pipe 17 only in the direction of arrow 15. Correspondingly, there is a check valve 19 interposed between pipe 20 and distributor 141 permitting passage of the fluid in pipe 20 only in the direction of arrow 16. Thus, chamber 13 can only be charged from pipe 17 and can discharge only into pipe 20.

Pipe 20, as indicated schematically is fluid-conductively connected to the inlet 21 of a tank or reservoir 22 only partially filled with the pumping fluid, for example, oil. The upper space, i.e., the space above the fluid level in reservoir 22 contains a gas such as air forming a cushion therein. The exit 23 of reservoir 22 is connected to a throttling nozzle 24 from which a line 25 is run to the load (not shown).

In FIG. 1 there are further shown electrical terminal lines 28 and 29 for coil 8 connecting it to a DC voltage source having a positive terminal 26 and a negative terminal 30. The positive voltage terminal 26, however, is not directly connected to terminal line 28, but there is interposed a pulse producing network 27. A rectifier 31 interconnects lines 28 and 29 at such a polarity, that for normal current conduction of the DC. voltage source, the rectifier is back biased.

The network 27 includes an electronic oscillator having an adjustable output frequency. During each cycle of the oscillator, there is a positive pulse running from terminal 26 to line 28, through coil 8, to line 29 and back into the DC. voltage source at its terminal 30; and there may be a corresponding pulse of opposite current conduction short circuited by rectifier 31 However, a positive D.C. component is superimposed upon the oscillation, so that, in fact, there is no negative half wave, but only a train of undirectional energizing pulses.

The positive pulses thus produced, energize electromagnet 89 periodically to correspondingly cause armature 6 of the pump to oscillate at a similar frequency. During the pause between two successive current pulses, coil 8 magnetically discharges through rectifier 31, and spring returns armature 6 into the illustrated position. Line 32 indicates, that, of course, oscillator of pulse source 27 is also connected to negative terminal 30 for completion of the electric circuit.

Proceeding now to FIG. 2, there is illustrated a circuit diagram for a pulse source 27. Coil 8 is illustrated only symbolically in this figure.

Portion a denotes a multivibrator connected to terminals 26 and 30 and including two p-n-p transistors 34 and 35 each. having its collector electrode capacitively connected to the base electrode of the respective other transistor (capacitors 39 and 41). Each transistor further has its emitter electrode directly connected to a common junction 36 connected to terminal 26. The collector electrodes are individually and resistively connected to the other voltage source terminal 30. The base electrodes are further resistively connected to junction 36, including individual resistors 38 and 40, and a common adjustable bias resistor 37.

Elements 37, 38 and 39 constitute an R-C coupling between the collector of transistor 35 and the common emitter junction, whereas elements 37, 40 and 41 constitute a corresponding R-C coupling for the collector of transistor 34. The adjustable resistor 37 permits adjustment of both R-C couplings so as to adjust the frequency of the multivibrator [1 within certain limits. These limits, however, yield a sufliciently large range for the specific purpose of utilizing the multivibrator in the instant case.

Terminal 42 at the collector electrode of transistor 35 denotes the specific output terminal for multivibrator a and there appears at this terminal 42 a train of rectangularly shaped voltage pulses.

This train of undirectional pulses is fed to a conventional transistor amplifier b in emitter configuration, the output of which is being fed to the base electrode of a transistor 44 pertaining to a second amplifier stage c. The collector electrode 43 of this amplifier c is directly connected to terminal line 28 leading to magnetizing coil 8 of the pump described in connection with FIG. 1.

As can be seen, coil 8 is interposed between the collector 43 and negative voltage source terminal 30, thus, being a component of the collector circuit of transistor 44. Rectifier 31 is connected across coil 8 in a direction opposite to the direction of permitted current conduction through p-n-p transistor 44.

The type of transistor employed is, of course, not critical, and the complementary type can be used while the poles of the voltage source and the polarity of the rectifier is being reversed.

Multivibrator a, thus, determines the rate of current pulses fed to coil 8, and upon proper adjustment of resistor 37, the pump armature 6 described with reference to FIG. 1 can be made to oscillate faster or slower accordingly. Hence, by adjusting resistor 37 it is possible to increase or to decrease the amount of fluid pumped.

Proceeding now to the next embodiment, FIG. 4 shall be described first. FIG. 4 illustrates a heating system employing a pump to be described with reference to FIG. 3. A subsurface tank 65 stores burner fluid such as oil, and there is an outlet standpipe 66 having inserted a pump 67 which is of the type to be described in connection with the detailed description of FIG. 3. A stove 68 contains a burner 69, into which is terminating pipe 66.

If the flame in burner 69 extinguishes accidentially, the continued flow of burner fluid runs into an overflow pipe 70 returning such fluid to the storage tank 65. Reference numeral 71 denotes a thermostat controlling a pulse source 72 at the stove and the pump 67. (See dashed lines.) This will be described in detail with reference to FIGS. 5 and 6.

Proceeding now to the description of the pump 67 shown in FIG. 3, there is a housing 45, with a yoke or core 46 coaxial and concentrical with respect to coil 8. Yoke or core 46 and coil 8 again constitute an electromagnet. Core 46 is threaded at its right end with which it is screwed into the right hand front wall of housing 45. The threaded portion of yoke 46 actually protrudes through this front wall, and a nut 47 secures the yoke 46 thereto. This mode of connecting yoke 46 to housing 45 permits a relative axial adjustment thereof, so that an adjustable air gap 48 is formed between the left hand face of yoke 46 and an armature plate 50. Armature plate 50 is secured to a membrane 51. Adjustment of air gap 48 is, of course, related to and contributes to the determination of the resting or zero position of the mechanically oscillating system to be described in the following:

Armature plate 50 is from its right hand side subjected to the force exerted thereupon by a tapered compression coil spring 52, engaging with its right hand end the easing for coil 8. Membrane 51 has a central bore receiving the left hand, threaded end of a guiding rod 53 having its right hand end slidingly extending into a nylon sleeve 54 so as to permit relative movement. Sleeve 54 in turn is received in a central bore 55 of core 46. The left hand, threaded end of rod 53, is screwed into a correspondingly threaded bore of a member 49. Thus, elements 49, 50, 51 and 53 constitute a compact unit capable of oscillating in common in axial direction.

The pressure and suction chamber proper 56 communicates with an antechamber 57, since the ring 58 of the radially narrowed housing 45 does not engage member 49 but there is a small, ring-shaped gap defined in between. Ring 58 is part of the inner wall of housing 45.

A rubber plate 59 is mounted on the left hand axially directed front of member 49. This plate 59 engages a valve seat 60 when no electric current flows in coil 8 and the oscillating unit as defined above is in resting or zero position. Valve seat 60 has an opening 61 which is the exit of a pressure line system 62 (correspnding to line 20 of FIG. 1). The check valve 19 is inserted in the line 62 for undirectionally blocking it. Valve 19 has a valve plate 63 engaging a corresponding valve seat 63a by gravitation normally as well as during the suction period. The closed position is shown in the drawing. Thus, line 62 is blocked during the suction period of the pump.

A suction line 64 leads laterally, i.e., axially displaced into antechamber 57 and contains the check valve 18. Check valve 18 has a valve plate 18a normally also resting by gravitation upon its associated valve seat 18b.

However, during suction period, this valve plate is lifted from its seat permitting connection of suction line 64 with feeder line 17. It should be noted, that lines 17, 62 and 64 are part of the line system 66 in FIG. 4.

The pump illustrated in FIG. 3 has the specific advantage as there is no open passage from the suction line to the pressure line or vice versa as long as no current flows through coil 8. This is of particular advantage if the oil burner fed by the pump has a burner bowl operating with evaporation. As is shown in FIG. 4 the oil is pumped by means of a pump as shown in FIG. 3 out of a lower position tank. If there were no blocking means provided between the lower suction line and the higher pressure line, all the oil in the system between tank and stove would run back into the tank due to gravity when the pump is at rest.

The membrane 51 in FIG. 3 could be substituted by a piston guided in a corresponding cylinder, whereby the piston is driven electromagnetically as described.

Proceeding now to FIG. 5, the content of the dashed rectangle illustrates the pulse source 72 of FIG. 4. This pulse source or pulse former is fed from a D.C. voltage supply source 73 connected to an A.C. voltage source such as the mains. The DC. supply source does not have to be as illustrated and in its simplest form may be constituted by a rectifier and filter capacitor.

In order to rectify small voltages at a sufiiciently high degree of efficiency, rectifier elements of very small inner resistivity have to be employed. The lowest resistance of all known rectifier elements is the collector-emitter path of a germanium power transistor. A circuit network using such transistors as rectifiers produces 24 volts at amp maximum output current. The power supply as illustrated includes a transformer, the primary of which is connected to the mains. A first, center tapped secondary winding has its outer branches resistively (90) connected to the base electrodes of tWo p-n-p transistors 89. The collector electrodes of the transistors are interconnected, whereas the emitter electrodes are respective ly connected to the outer branches of a second, center tapped secondary transformer winding. The center tap of the latter winding is connected to one side of a choke 91, the other side of which constitutes the minus pole of D.C. source 73. The center tap of the first secondary constitutes the plus pole of D.C. source 73. The transis-- tors 89 of type ADlO3 serve as controlled rectifiers. Adjustable resistors 90 serve for adjusting the network to symmetrical operation. Since the circuit network 73 is a rectifier, transistors 89 have to be rendered conductive and nonconductive periodically at the rate of the AC. input frequency. The choke 91 causes the output voltage to have only very slight ripples and even though transistors 89 are controlled by a sinusoidal voltage, the alternating collector current pulses are highly rectangular. This, of course, requires the transistors to be controlled so as to rapidly assume saturation, i.e., the control voltage must be correspondingly high.

Pulse source 72 includes a multivibrator but being formed by a different network as compared with FIG. 2. The multivibrator in FIG. 5 includes two transistors 78 and 87, with the collector electrode of n-p-n transistor 78 being resistively connected to the base electrode of p-n-p transistor 87, whereas the collector electrode of transistor 87 is connected to the base electrode of transistor 78 via a series circuit connection of a resistor 88 and of a capacitor 86. Due to the different types of transistors employed, their emitter electrodes are not interconnected, but the emitter electrode of transistor 87 is connected to the plus pole and the emitter electrode of transistor 78 is connected to the minus pole of source 73.

Pump coil 8 is connected on one side to the minus pole and through the emitter-collector path of transistor 87 to the plus pole of source 73.

The astable multivibrator as disclosed having a pair of complementary transistors has an exceptionally high efiiciency, and it can produce pulses of long duration at relatively small oscilliator capacity whereas the pulses have a very sharp rectangular shape. Since both transistors are non-conductive between two pulses, an efficiency is attained of up to 95 to 98 In order to explain the operation of the multivibrator, it shall be assumed that both transistors are nonconductive and, thus, there is a pulse pause. Transistor 78 being, for example, of the n-p-n type BCY13, remains nonconductive until the voltage across capacitor 86 has reached the knee voltage of the base emitter diode of transistor 78. Capacitor 86 charges through the pumping magnet coil 8, and resistors 76, 37 and 88. However, the charging current is very small so as not to cause energization of the pump. Having reached this knee voltage, a small base current flows in transistor 78 which is amplified therein by current amplification and the amplified current controls transistor 87 (p-n-p type TF78). The increasing voltage drop across coil 8 causes the collector potential to shift towards positive values. Resistor 88 and capacitor 86 operate as a feedback loop rapidly increasing the base current in transistor 78. Thus, by regenerative feedback action, both transistors are soon conductive to saturation and full current flows through coil 8 causing the pumping magnet to be energized.

The capacitor 86 now discharges through resistor 88 and the base-emitter path of transistor 78. When the capacitor 86 has discharged to such an extent, that the base current in transistor 78 is insufficient to maintain collector saturation both transistors are returned to nonconduction.

It appears that resistors 76 and 37' are primarily responsible for the duration of a pause between two succeeding current pulses, whereas resistor 88 primarily determines current pulse duration.

The decreasing of the collector potential of transistor 87 towards negative values is again coupled by feedback action of resistor 88 and capacitor 86 to the base electrode of transistor 78, so that again the state of nonconduction for both transistors is regeneratively attained at a rapid rate.

As compared with pulse duration and pause, the pulse flanks can be considered as being vertical due to this rapid regenerative feedback action so that for all practical purposes the pulse blocks are rectangular indeed. Switching losses in the transistors are negligibly small.

Base electrode of transistor 78 is connected to the said plus pole via a constant resistor 76 in series with a variable resistor or rheostat 37. This variable resistor 37' corresponds in function to resistor 37 of FIG. 2 in that both determine and adjust the multivibrator frequency. Resistor 37' is shown as having a rotary slider 77 for adjustment connected to a terminal 74 which in turn is connected to the said plus pole.

In its left hand terminal position, slider 77 directly connects resistor 76 to terminal 74 and the plus pole. At such slider position only resistor 76 determines the time constant of the R-C circuit network of the multivibrator and the frequency therein. Since this time constant is small, the multivibrator frequency is correspondingly high, and the pump controlled by pulse source 72 advances at maximum controlled capacity.

Normally, one will select a position for slider 77 so that there is a medium multivibrator frequency, i.e., a portion of resistor 37' is added to resistor 76 and the time constant is correspondingly longer but not of maximum duration as adjustable with slider 77. This results in a flame corresponding to a particular average season.

Thermostat 71 senses room temperature and governs contacts capable of overbridging resistor 37' or whatever portion thereof is connected between the plus pole and resistor 76. For example, upon closing contacts 85, the thermostat causes the multivibrator to operate at maximum frequency and, 'hence the pump conveys maximum burner fluid to the stove. Thus, the stove normally produces a certain .amount of heat, but if the room temperature falls below a certain level, the heat production is momentarily increased. When the room temperature is raised sufiiciently, thermostat 71 opens contacts 85 and the multivibrator, pump and stove resume normal operation as determined by the previously made adjustment of resistor 37. The stove, therefore, is not operated in an on-ofi? manner but intermittently, with alterntaing between normal and accelerated burning rates, whereby the accelerated mode constitutes maximum operational speed orpower output.

Reference numeral 79a denotes schematically a ganging connection between slider 77 of resistor 37' and the slider of another adjustable resistor 79. This resistor 79 is connected in series with a blower 80 fed from the AC). mains. The blower speed is, thus, adjusted together with the multivibrator-stove-burner speed in that the blower speed is increased with increasing multivibrator frequency, i.e., with increasing power output of the burner. One can see from the drawing, that both sliders will be rotated clockwise for decreasing both, blower speed and burner output. It is possible to employ a DC. motor for the motor and to use rheostat 79 as controlled series or shunt resistor, with either armature or field control.

The thermostat, correspondingly governs another set of contacts 81 which when closed bridge whatever portion of resistor79 has been placed in circuit with the blower. Thus, when contacts 81 have been closed, the blower operates at maximum speed and at the same time a closing of contacts 85 has caused the oscillator to produce maximum frequency; the burner operates at maximum power output correspondingly.

It should be mentioned, that a blower such as 80 is not essential and will be used only when there is poor draft in the stove.

FIG. 6 illustrates a modification of the thermostatmultivibrator control as described with reference to "FIG. 5. Rheostat 37" corresponds generally to resistor 37' in FIG. 5, but upon rotating slider 77" (arrow .82), fixed resistors 83 are stepwise added or subtracted from the resistive series circuit determining the multivibrator frequency, and this frequency is, thus, being altered stepwise. The illustrated position of slider 77" is the one in which all of the resistors 83 are out. However, in this embodiment, there is shown a resistor 84 to remain incircuit with resistor 76, and only when the contacts85 of thermostat 71' close, this resistor 84 is also out of circuit. Thus, maximum multivibrator frequency and maximum power output of the burner is not adjustable with the rheostat but only controllable by the thermostat. This way accidental overheating is prevented.

The heating system controlled by the device shown in FIG. can be modified in that the contacts 85 of the thermostat control an electromotor in any kind of motor driven pump, so that the thermostat causes this motor to alternate between maximum and adjustable average speed and corresponding pumping output.

The units 72 and 67 will thereby be substituted by an electromotor with adjustable power output, and the motor shaft thereof is drivingly coupled to the pumping shaft. Particularly the thermostat contacts are to overbridge a series resistor in the motor energizing circuit. Thus, here also the pump is alternated between maximum and adjustable average power output.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departments from the spirit and scope of the invention are intended to be covered by the following claims:

What is claimed is:

1. A control system for an oil burner comprising an electrically operable variable speed blower for delivering air to said burner, and an electromagnetic pump for delivering fuel to said burner, an electric impulse generator for supplying a pulsating current to said pump, said impulse generator comprising a two transistor oscillation circuit, a pair of variable resistance means respectively regulating the speed of said blower and the frequency of said pulsating current, and thermostat means having switch contacts effecting alternate switching in and out of said resistance means .to effect variations of speed of said blower and variations in stroke frequency of said pump.

2. A control system for oil burners as defined in claim 1, said two transistor oscillation circuit including circuit means connected to form an astable multivibrator.

3. A control system as defined in claim 2, wherein means are provided to create an isolation between the magnetic discharge of said electromagnetic pump and said astable multivibrator.

4. A control system as defined in claim 1, wherein the switching effects of said thermostat means increase the speed of the blower with higher frequency anddecrease the speed with the lower frequency.

References Cited by the Examiner UNITED STATES PATENTS 1,359,042 11/ 1920 Doble. 2,029,374 2/ 1936 Houston. 2,149,545 3/1939 Price. 2,393,167 1/1946 Holthouse 126110 2,472,067 6/1949 Dickey et al. 2,569,877 10/1951 Woodruff. 2,581,942 1/1952 Collins et al. 2,646,931 7/1953 Suter 23649 2,681,695 6/1954 Bills et al. 15836.3 X 2,722,180 11/1955 McIlvaine 1584 X 2,933,051 4/ 1960 Toulmin 10353 3,070,024 12/ 1962 Romberg 103-53 3,118,383 1/1964 Woodward 10353 FREDERICK L. MATTESON, 111., Primary Examiner. JAMES W. WESTHAVER, Examiner. 

1. A CONTROL SYSTEM FOR AN OIL BURNER COMPRISING AN ELECTRICALLY OPERABLE VARIABLE SPEED BLOWER FOR DELIVERING AIR TO SAID BURNER, AND AN ELECTROMAGNETIC PUMP FOR DELIVERING FUEL TO SAID BURNER, AN ELECTRIC IMPULSE GENERATOR FOR SUPPLYING A PULSATING CURRENT TO SAID PUMP, SAID IMPULSE GENERATOR COMPRISING A TWO TRANSISTOR OSCILLATION CIRCUIT, A PAIR OF VARIABLE RESISTANCE MEANS RESPECTIVELY REGULATING THE SPEED OF SAID BLOWER AND THE FREQUENCY OF SAID PULSATING CURRENT, AND THERMOSTAT MEANS HAVING SWITCH CONTACTS EFFECTING ALTERNATE SWITCHING IN AND OUT OF SAID RESISTANCE MEANS TO EFFECT VARIATIONS OF SPEED OF SAID BLOWER AND VARIATIONS IN STROKE FREQUENCY OF SAID PUMP. 